1. Field of the Invention
The present invention relates to an ink-jet recording apparatus for recording an image by ejecting ink within an ink cartridge onto a recording medium via nozzles of a recording head, and more particularly to a circuit for detecting whether or not a recording head is being driven.
2. Description of the Related Art
In recording an image on a recording medium such as a sheet of paper or an overhead projection film, recording systems such as a wire dot system, a thermal transfer system and an ink jet system generally utilize their own recording heads. Among the above-stated recording systems, the ink jet system is for recording an image by directly ejecting ink onto a recording medium. A recording apparatus employing the ink jet system has a recording head arranged with a plurality of nozzles formed with minute ejection holes for ejecting the ink. The ink within the nozzles is heated by heating elements installed in respective nozzles, thereby expanding the ink so as to be ejected out of the nozzles. By this operation, the heating elements are selectively driven to record a desired image onto the recording medium.
If a circuit for driving the heating elements breaks down, the ink within a corresponding nozzle or nozzles is not ejected to thereby impede the recording of an image or to degrade the picture quality. In this case, earlier systems have heretofore detected the failure in the driving of the recording head and informed a user of the detection, thereby causing the user to replace the recording head. For this operation, an ink jet recording apparatus is provided with a recording head driving detection circuit as shown in FIG. 1 to detect whether or not the recording head is being driven. In FIG. 1, a plurality of heating elements RT1.about.RTn are installed to respectively correspond to nozzles (not shown) of the recording head, and heat the ink so as to eject the ink within the corresponding nozzles when being driven by a driving means 2. The driving means 2 includes a plurality of resistors RB1.about.RBn, a plurality of transistors Q1.about.Qn and a driving circuit 8 for driving the heating elements RT1.about.RTn in correspondence with nozzle driving data ND supplied from a processor 6. Resistors RB1.about.RBn are respectively connected between a driving power source voltage Vpp and one respective end of each of the heating elements RT1.about.RTn, and transistors Q1.about.Qn are respectively connected between the other respective ends of the heating elements RT1.about.RTn and ground. Driving circuit 8 is connected between respective bases of transistors Q1.about.Qn and the processor 6. Transistors Q1.about.Qn supply the driving power source voltage Vpp to corresponding heating elements among the heating elements RT1.about.RTn in accordance with a signal supplied to respective bases from the driving circuit 8, thereby driving corresponding nozzles. A driving detecting circuit 4 is formed by a plurality of diodes D1.about.Dn, a Zener diode ZD1, two resistors R1 and R2, a transistor Qa and a D flip-flop 10. Processor 6 drives heating elements RT1.about.RTn via the driving means 2, and detects whether the recording head is driven or not based upon a logic level of a detection signal DET from the D flip-flop 10 of driving detecting circuit 4, and supplies a clear signal CLR to the D flip-flop 10 to clear it.
An operation of the recording head driving detection circuit as shown in FIG. 1 will be described with reference to FIG. 2 showing operational timing charts of respective parts shown in FIG. 1 and FIG. 3 showing the flowchart of the operation of the processor 6.
First, at the point prior to enabling nozzle driving data ND, transistors Q1.about.Qn are in the turned off state and, accordingly, diodes D1.about.Dn are in the turned off state. Therefore, a voltage Va at a junction point of diodes D1.about.Dn and Zener diode ZD1 goes to a high level as shown in FIG. 2. Thus, transistor Qa is in the turned on state and an output voltage Vb of a collector of transistor Qa is supplied to a clock terminal of D flip-flop 10 at a low level as shown in FIG. 2. At this time, D flip-flop 10 is cleared by a clear signal CLR of the processor 6 after initialization or previous recording head driving, and maintains the stand-by state.
Under the above-described state, the processor 6 generates nozzle driving data ND corresponding to image data to be recorded and provides it to the driving means 2 in step 300, and checks the logic level of the detection signal DET received via the detecting circuit 4 in step 302. Here, it is assumed that nozzle driving data ND is enabled from a point to during an interval Te as shown in FIG. 2. Driving circuit 8 drives heating elements RT1.about.RTn to correspond to nozzle driving data ND for enable interval Te. That is, transistors Q1.about.Qn are selectively turned on in accordance with nozzle driving data ND to force the driving power source voltage Vpp to be applied to corresponding heating elements. By doing so, corresponding heating elements are heated, which in turn heats the ink within the corresponding nozzles to enable ejection. Among diodes D1.about.Dn, diodes connected to transistors via the heating elements are turned on at this time. By this operation, the level of voltage Va at the junction point of diodes D1.about.Dn and Zener diode ZD1 becomes low at point to as shown in FIG. 2. Then, transistor Qa is turned off to permit the output voltage Vb of the collector of transistor Qa to transit from the low to the high at point to as shown in FIG. 2, thereby being supplied to D flip-flop 10 as a clock. The D flip-flop 10 latches a high of a power source voltage Vcc at the rising edge of voltage Vb to provide a detection signal DET to point to of FIG. 2 at the high level. Here, if any of the heating elements RT1.about.RTn or transistors Q1.about.Qn for driving heating elements RT1.about.RTn and driving circuit 8 are broken, the detection signal DET continuously maintains the low level.
Thus, the processor 6 generates nozzle driving data ND in step 300, and checks the logic level of detection signal DET in step 302, so that the driving of heating elements RT1.about.RTn, i.e., the recording head, can be detected. If detection signal DET is at a low level, it means that it has been determined that the recording head is not being driven so that it is necessary to execute error processing. The error processing is performed to inform the user of the failure in such a manner that the operation is stopped to display a message indicating the failure of the recording head. When the detection signal DET of a high level is received at point to, it means that the recording head is being driven. After this, a low clear signal CLR having a prescribed pulsewidth is provided to D flip-flop 10 at point t1 as shown in FIG. 2, thereby clearing the D flip-flop 10 in step 304.
The above-described operation is repeatedly carried out whenever the recording head is driven to continuously detect whether or not the recording head is being driven.
The processor 6 checks whether or not the recording head is driven by means of detection signal DET whenever the recording head is driven to clear the D flip-flop 10 by the clear signal CLR so that the processing time and load required for detecting the driving of the recording head are greatly increased.
Consequently, there is heretofore a drawback in that the increased processing time and load required for detecting the driving of the recording head as described above slows down performance, i.e., the printing speed.
Meantime, an ink jet recording apparatus utilizing a recording head of the disposable type tends to be gradually accepted for general use. In the disposable type of head, the recording head is integrally provided with an ink cartridge to be disposed altogether when the ink within the ink cartridge is thoroughly consumed. Frequently, in replacing the recording head, the ink jet recording apparatus is often operated while a user has not yet mounted a new recording head by mistake after removing the used recording head. Thus, the recording operation is performed in spite of a lack of a recording head. For this reason, a detection pin is separately installed on the ink cartridge or recording head for detecting the existence of the recording head in the corresponding apparatus, and the detection pin is utilized to detect whether or not the recording head has been mounted. However, it is disadvantageous in that the detection pin must be separately installed and additionally requires a line for connecting to the ink cartridge or recording head, and the number of pins of a connector is increased.